[MERGE #5318 @mike-kaufman] fixing bug where page de-alloc stats weren't being initialized

Merge pull request #5318 from mike-kaufman:build/mkaufman/fix-uninitialized-struct-for-page-de-allocation-stats

Author: Mike Kaufman

lib/Common/Memory/AllocatorTelemetryStats.h

@@ -14,6 +14,15 @@ struct AllocatorDecommitStats
     int64 numDecommitCalls;
     int64 numPagesDecommitted;
     int64 numFreePageCount;
+
+    AllocatorDecommitStats() :
+        lastLeaveDecommitRegion(),
+        maxDeltaBetweenDecommitRegionLeaveAndDecommit(0),
+        numDecommitCalls(0),
+        numPagesDecommitted(0),
+        numFreePageCount(0)
+    {}
+
 };
 
 struct AllocatorSizes

lib/Common/Memory/PageAllocator.cpp

@@ -1948,10 +1948,13 @@ PageAllocatorBase<TVirtualAlloc, TSegment, TPageSegment>::DecommitNow(bool all)
     if (this->decommitStats != nullptr)
     {
         this->decommitStats->numDecommitCalls++;
-        Js::TickDelta delta = Js::Tick::Now() - this->decommitStats->lastLeaveDecommitRegion;
-        if (delta > this->decommitStats->maxDeltaBetweenDecommitRegionLeaveAndDecommit)
+        if (this->decommitStats->lastLeaveDecommitRegion.ToMicroseconds() > 0)
         {
-            this->decommitStats->maxDeltaBetweenDecommitRegionLeaveAndDecommit = delta;
+            Js::TickDelta delta = Js::Tick::Now() - this->decommitStats->lastLeaveDecommitRegion;
+            if (delta > this->decommitStats->maxDeltaBetweenDecommitRegionLeaveAndDecommit)
+            {
+                this->decommitStats->maxDeltaBetweenDecommitRegionLeaveAndDecommit = delta;
+            }
         }
     }
 #endif